By placing a plurality of wafer-shaped substrates in a bath in which a chemical solution is stored, multiple substrates may be etched at the same time. In this process, the chemical solution may flow on a respective surface of each substrate. At this time, if the flow velocity of the chemical solution flowing on the surface of each substrate is nonuniform between the substrates, an etching amount tends to differ between the substrates.
A method of generating bubbles in the chemical solution can be implemented to help make the flow velocity of the chemical solution uniform among substrates. When this method is used, if the generation state of bubbles (e.g. the rate at which bubbles are being generated) is not controlled, the nonuniformity of the flow velocity of the chemical solution may not be eliminated, and the etching amount may still differ among the substrates.